Precise control of RF voltage applied to a quadrupole in mass spectrometer is generally desirable as the applied RF voltage generally contributes to the ejection and/or filtering of ions in the quadrupole. Hence, the precision to which RF voltage is applied affects the accuracy and reliability of the quadrupole. In order to control the RF voltage, the RF voltage is generally measured via an RF detector and an RF power source controlled in a feedback loop with the RF detector. FIG. 2 depicts an RF detector according to the prior art in which a rectifying diode array is used to measure RF voltage in combination with an averaging circuit, such as an RC filter, for providing an average of the rectified RF voltage. However, such an RF detector suffers from reverse leakage current in the diodes, which in turn leads to instability in the detector resulting in mass drift in the quadrupole and breakdown of the diodes.